Japanese Patent Laid-Open No. 2002-303177 discloses technology (hereunder, referred to as “related art”) relating to throttle control in an internal combustion engine equipped with an electronic throttle. In the internal combustion engine of the related art, the requested torque which should be generated by combustion of the internal combustion engine is calculated based on the accelerator operation of a driver and the like, and the target in-cylinder charging air amount is calculated based on the requested torque, and the target intake pressure is calculated based on the target in-cylinder charging air amount and engine speed. Subsequently, the target degree of throttle opening is calculated based on the target in-cylinder charging air amount and the target intake pressure, and the actuator of the throttle is controlled based on the target degree of throttle opening.
Further, the internal combustion engine of the above described related art is equipped with an EGR device for recirculating part of the exhaust gas to the intake side. An exhaust gas recirculation amount (an EGR flow rate) is a parameter of the variation factor of the intake pressure. Therefore, in the internal combustion engine of the above described related art, the target intake pressure is corrected by using an EGR flow rate.
Incidentally, there has been conventionally known an internal combustion engine capable of performing switching control of an air-fuel ratio such as switching from the operation by a theoretical air-fuel ratio to the operation by an air-fuel ratio leaner than the theoretical air-fuel ratio, or switching in the opposite way. Paying attention to the EGR control of the internal combustion engine like this, the EGR rate to be a target (the target EGR rate) is also switched with switching of the air-fuel ratio. However, even when the EGR rate to be the target is switched, the actual EGR rate (the real EGR rate) does not change immediately. This is because there arise a delay in response of an actuator (an EGR valve) that regulates the EGR rate, and a delay in response corresponding to the volumetric capacity of the EGR route from the EGR valve to the throttle. If air with an EGR rate higher than the target EGR rate is taken into the cylinder due to the delays in response, there arises the risk of occurrence of a misfire and an engine stall.